This invention relates to a bearing thrust monitoring assembly and a method for aligning a bearing configured to support a rotary body, particularly a large rotary body such as a hot, rotary kiln.
Large rotating cylinders are used in carrying out a large number of economically important processes. Such rotary, trunnion supported equipment typically includes a steel tube that may be quite long (up to several hundred feet in length), and that is supported by annular tires spaced along the length of the tube. Each tire is carried on a pair of opposed rollers, which in turn may be mounted upon a concrete pier or pad. The steel tube is rotated about its longitudinal axis, and is supported for such rotation by contact of the rollers with the tires surrounding the tube. The rollers are supported upon the piers or pads by roller support bearings. These are typically sleeve bearings on the larger equipment and antifriction bearings on smaller sized equipment. Due to the wear and tear of the roller support bearings, the rollers, and the tires, and distortion of various parts of the system (including possible movement of the piers or pads upon which such rotary equipment is mounted), the rollers can get out of alignment so as to cause portions of the equipment to rotate about different rotational axes. Since the cost of replacing the tires or rollers, or both, is relatively high, an important consideration in the operation of such rotary equipment is the maintenance of proper alignment between the surface of a roller and the supporting tire to prevent uneven wearing of the respective surfaces and overloading the bearings. If the two are kept in proper alignment, a long life can be expected from the tire and the rollers and the bearings.
Alignment relationships are complicated by the fact that such rotary equipment is typically constructed with the tube on a slight slope relative to horizontal to facilitate the flow of material therethrough. Thus, the tube exerts an axial force due to gravity (as well as other axial loads that may be place upon it in operation), thereby causing an axial thrust load to exist on the rollers and their associated roller support bearings whenever they are required to counteract gravity to keep the tube running on the rollers. In order to maintain proper alignment between the tube and roller support bearings, it has previously been necessary to periodically check the alignment by visual inspection or by sophisticated alignment measurements, to determine roller axial position as best possible. But since such measurements can never be accurate enough, incremental roller adjustments for skew are made until the roller shifts axially into a desired position that is approximately parallel with the axis of the tube. Sleeve bearing arrangements are configured to allow an axial shift of the roller and shaft assembly of approximately 6 mm for this purpose. In this way, the skew adjustment causes this axial shift whenever the neutral skew position is crossed. However, this method is inadequate whenever antifriction bearings are employed, because they are required to be locked to the roller shaft either by shrinking or other mechanical means. No allowance for physical axial shift between the bearing and shaft exists. Since the amount of skew adjustment to cause a roller to shift axially is on the order of 0.1 mm (0.004 inches) no matter what size of roller, even as large as 10 feet in diameter, it is all but impossible to measure skew since the axis of rotation of the tube can never by physically established to that fineness. Since antifriction bearings by their very design do not allow any such axial shift, the checks must be made relatively often, are difficult to evaluate, very subjective, and in most instances are not dependably carried out by the operator.